Present value$($with changing interest$$ rates$).$Marty has been offered an injury settlement of $$$$8$ comma $000$ payable in $4$ years. He wants to know what the present value of the injury settlement is if his opportunity cost is $4\mathrm{.}5\%.($The opportunity cost is the interest rate in this$$ problem.$)$ What if the opportunity cost is $7\%?$ What if it is $10\mathrm{.}5\%?$